Background of the Invention
The present invention relates to a transmission for vehicle that includes a hydraulic pump body and a hydraulic motor body, and an auxiliary pump for replenishing operational fluid to flow therebetween.
It is known from such as Japanese Patent Application Laid-open No. Hei-11-91379 that a transmission housing is also used as a part of a vehicle frame to simplify the vehicle structure and reduce the manufacturing cost.
According to the arrangement described in the above cited publication, along with the transmission housing a center section that supports thereon a hydraulic pump and a hydraulic motor also makes up a part of the vehicle frame. This arrangement poses a problem as described below.
The center section is originally intended to support thereon the hydraulic pump and the hydraulic motor, as well as serving as a fluid circuit for HST operational fluid that circulates between the hydraulic pump and hydraulic motor. Therefore, it may be sufficient for the center section to be tolerable against the total weight of the hydraulic pump and the hydraulic motor and have such a stiffness as to be tolerable against the maximum preset hydraulic pressure in the fluid circuit.
However, as described in the above-cited publication, where the center section is connected to the transmission housing via their connecting portions under an exposed condition, their connecting portions each are subjected to bending stress due to the weight of a driver supported by a vehicle body frame, and that of vehicle components mounted on or towed by the vehicle body frame.
Therefore, with the arrangement described in the above-cited publication, the center section is required to have a higher stiffness than originally required. This poses a problem that the manufacturing cost cannot be substantially reduced whether a part of the vehicle body frame is made up of the transmission housing for reduction of the cost.
In the transmission described in the above-cited publication, the hydraulic pump and the hydraulic motor are arranged in parallel along a vehicle width direction. This arrangement necessitates a longer distance between a pump shaft of the hydraulic pump and a motor shaft of the hydraulic motor, and hence poses a problem of inviting larger-sizing of the transmission itself.
In the transmission of the above type, an auxiliary pump for replenishing operational fluid between the hydraulic pump and the hydraulic motor must be mounted to an input shaft of the HST or the pump shaft. Accordingly, to reduce the size of the transmission, it is required to take the existence of the auxiliary pump into consideration. However, it is apparent that the transmission of the above-cited publication was designed with no consideration for addressing this matter.
The present invention has been thus conceived in consideration of the above prior art. It is an object of the present invention to provide a transmission that is capable of being manufactured in reduced size, while achieving a relatively low manufacturing cost of the center section that supports thereon the hydraulic pump body and the hydraulic motor body.
It is another object of the present invention to provide a transmission that allows the adjustment of the HST to be performed by independent adjustment of the HST itself, while achieving the above object.
To achieve the above objects, there is provided a transmission for vehicle with an HST interposed in a drive power transmission path that includes: a housing; a center section having a plate-like shape with a first surface and a second surface opposite to the first surface with respect to a drive power transmission direction, and the center section being disposed within the housing; an input shaft extending through the center section; an output shaft disposed parallel with the input shaft and away from the same in a plate surface direction of the center section; a hydraulic pump body supported on the first surface of the center section and operatively connected to the input shaft; a hydraulic motor body supported on the second surface of the center section and being adapted to drive the output shaft upon receiving operational fluid discharged from the hydraulic pump body; a bearing plate fixed within the housing, facing either one of the first and second surfaces of the center section for supporting the input shaft; and an auxiliary pump disposed on the bearing plate and being adapted to be driven through the input shaft.
With the transmission having the above arrangement, the distance between the input shaft and the output shaft can be minimized as much as possible, even if the transmission is provided with the auxiliary pump. Thus, the transmission can be manufactured in reduced size.
In the transmission for vehicle having the above arrangement, the input shaft preferably has a downstream end with respect to the drive power transmission direction, which downstream end of the input shaft extending through the center section and being operatively connected to a PTO shaft.
With this arrangement, the drive power transmission path of the PTO can be efficiently arranged.
The transmission for vehicle preferably has the housing that includes a flywheel housing for accommodating a flywheel, and a an intermediate housing joined to the flywheel housing; the center section that is designed to be fixed to the flywheel housing or the intermediate housing in proximity to a joined portion between the flywheel housing and the intermediate housing, while supporting the hydraulic pump body and the hydraulic motor body; and the hydraulic pump body, the hydraulic motor body and the center section are enclosed within an accommodation member made up of the flywheel housing and the intermediate housing when both the housings have been joined together.
With the above arrangement, even in case that the housing is used as a part of the vehicle body frame, bending stress can effectively be prevented from applying on the hydraulic pump body, the hydraulic motor body and the center section. Hence, the manufacturing cost of the center section can be reduced.
In the above arrangement, the center section with the hydraulic pump body and the hydraulic motor body supported thereon is fixed to the flywheel housing or the intermediate housing, in which the hydraulic pump body and the hydraulic motor body respectively and inherently have casings. This arrangement enables the HST to be independently assembled, thereby achieving improved operational efficiency in adjusting the HST and incorporating the same in the transmission.
Also, in the above arrangement, the hydraulic pump and the hydraulic motor are enclosed with a double layer of wall, namely the exclusively designed casings respectively provided on the hydraulic pump body and the hydraulic motor body, and the flywheel housing or the intermediate housing. Whereby, improved noise reduction effect can be achieved.
According to another aspect of the present invention, there is provided a transmission for vehicle with an HST and a power shift device interposed in tandem in a drive power transmission path that includes: a housing; first and second plate-like members disposed within the housing in such a manner as to be positioned away from each other along a drive power transmission direction, while respectively having each-other facing surfaces, through which the first and second plate-like members face each other; an input shaft extending through the first plate-like member; an output shaft disposed parallel with the input shaft and away from the same in a plate surface direction of the first plate-like member; a hydraulic pump body supported on a surface opposite to the each-other facing surface of the first plate-like member, and operatively connected to the input shaft; a hydraulic motor body supported on the each-other facing surface of the first plate-like member, and being adapted to drive the output shaft upon receiving operational fluid discharged from the hydraulic pump body; an auxiliary pump disposed on the second plate-like member and being adapted to be driven through the input shaft; and wherein the second plate-like member supports thereon a clutch shaft of the power shift device, and has a hydraulic fluid passage for supplying therethrough pressurized hydraulic fluid discharged from the auxiliary pump to a hydraulic clutch on the clutch shaft.
With the transmission having the above arrangement, the distance between the input shaft and the output shaft can be minimized as much as possible, even if the transmission is provided with the auxiliary pump. Thus, the transmission can be manufactured in reduced size.
In addition, the hydraulic fluid passage from the auxiliary pump to the hydraulic clutch can be shortened.
The input shaft preferably has a downstream end with respect to a drive power transmission direction, the downstream end of the input shaft extending through the center section and being operatively connected to a PTO shaft.
With the above arrangement, the drive power transmission path of the PTO can efficiently be arranged.
The output shaft and the clutch shaft are preferably disposed coaxial with each other and are relatively non-rotatably connected to each other.
The transmission for vehicle is preferably arranged so that the housing includes a flywheel housing for accommodating a flywheel, an intermediate housing joined to the flywheel housing and a clutch housing joined to the intermediate housing for accommodating the power shift device; the first plate-like member is designed to be fixed to the flywheel housing or the intermediate housing in proximity to a joined portion between the flywheel housing and the intermediate housing, while supporting the hydraulic pump body and the hydraulic motor body; the second plate-like member is designed to be fixed to the intermediate housing and the clutch housing in proximity to a joined portion between the intermediate housing and the clutch housing; the hydraulic pump body, the hydraulic motor body and the first plate-like member are enclosed within an accommodation member made up of the flywheel housing and the intermediate housing when both the housings have been joined together; and the second plate-like member is enclosed within an accommodation member made up of the intermediate housing and the clutch housing when both the housings have been joined together.
With the above arrangement, even in case that the housing is used as a part of the vehicle body frame, bending stress can effectively be prevented from applying on the hydraulic pump body, the hydraulic motor body, the first plate-like member and the second plate-like member. Hence, the manufacturing costs of the first plate-like member and the second plate-like member can be reduced.
In the above arrangement, the first plate-like member with the hydraulic pump body and the hydraulic motor body supported thereon is fixed to the flywheel housing or the intermediate housing, in which the hydraulic pump body and the hydraulic motor body respectively and inherently have casings. This arrangement enables the HST to be independently assembled, thereby achieving improved operational efficiency in adjusting the HST and incorporating the same into the transmission.
The hydraulic pump and the hydraulic motor are also enclosed with a double layer of wall, namely with the exclusively designed casings respectively provided on the hydraulic pump body and the hydraulic motor body, and the flywheel housing or the intermediate housing. Whereby, improved noise reduction effect can be achieved.
The transmission for vehicle preferably further includes a PTO shaft disposed coaxial with the input shaft and operatively connected to the same, and the driven shaft has a hollowed body, into which the PTO shaft is inserted.
According to this arrangement, although the transmission has a three-shaft-construction with the clutch shaft, driven shaft and PTO power transmission shaft, it can be constructed as having substantially two shafts, so that the transmission itself can be manufactured in reduced size.
In the transmission for vehicle with the HST and the power shift device interposed in tandem in a drive power transmission, the power shift device may include a driven shaft disposed substantially parallel to the clutch shaft and a plurality of hydraulic clutches for stepwisely changing the speed of the drive power between the clutch shaft and the driven shaft, in addition to the clutch shaft that is disposed coaxial with the output shaft and relatively non-rotatably connected to the same.